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How to convert a Roman numeral to integer in PHP?

由 隐身守侯 提交于 2019-11-27 11:12:20

问题


Using PHP, I'd like to convert a string containing a Roman number into its integer representation. I need this because I need to make calculations on them.

Wikipedia on Roman numerals

It would suffice to only recognize the basic Roman numeral characters, like:

$roman_values=array(
    'I' => 1,
    'V' => 5,
    'X' => 10,
    'L' => 50,
    'C' => 100,
    'D' => 500,
    'M' => 1000,
);

That means the highest possible number is 3999 (MMMCMXCIX). I will use N to represent zero, other than that only positive integers are supported.

I cannot use the PEAR library for Roman numbers.

I found this great question on SO on how to test whether the string contains a valid Roman numeral:

How do you match only valid roman numerals with a regular expression?

What would be the best way of coding this?


回答1:


How about this:

$romans = array(
    'M' => 1000,
    'CM' => 900,
    'D' => 500,
    'CD' => 400,
    'C' => 100,
    'XC' => 90,
    'L' => 50,
    'XL' => 40,
    'X' => 10,
    'IX' => 9,
    'V' => 5,
    'IV' => 4,
    'I' => 1,
);

$roman = 'MMMCMXCIX';
$result = 0;

foreach ($romans as $key => $value) {
    while (strpos($roman, $key) === 0) {
        $result += $value;
        $roman = substr($roman, strlen($key));
    }
}
echo $result;

which should output 3999 for the supplied $roman. It seems to work for my limited testing:

MCMXC = 1990
MM = 2000
MMXI = 2011
MCMLXXV = 1975

You might want to do some validation first as well :-)




回答2:


I am not sure whether you've got ZF or not, but in case you (or any of you who's reading this) do here is my snippet:

$number = new Zend_Measure_Number('MCMLXXV', Zend_Measure_Number::ROMAN);
$number->convertTo (Zend_Measure_Number::DECIMAL);
echo $number->getValue();
  • Zend_Measure_Number on framework.zend.com



回答3:


This is the one I came up with, I added the validity check as well.

class RomanNumber {
    //array of roman values
    public static $roman_values=array(
        'I' => 1, 'V' => 5, 
        'X' => 10, 'L' => 50,
        'C' => 100, 'D' => 500,
        'M' => 1000,
    );
    //values that should evaluate as 0
    public static $roman_zero=array('N', 'nulla');
    //Regex - checking for valid Roman numerals
    public static $roman_regex='/^M{0,3}(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$/';

    //Roman numeral validation function - is the string a valid Roman Number?
    static function IsRomanNumber($roman) {
         return preg_match(self::$roman_regex, $roman) > 0;
    }

    //Conversion: Roman Numeral to Integer
    static function Roman2Int ($roman) {
        //checking for zero values
        if (in_array($roman, self::$roman_zero)) {
            return 0;
        }
        //validating string
        if (!self::IsRomanNumber($roman)) {
            return false;
        }

        $values=self::$roman_values;
        $result = 0;
        //iterating through characters LTR
        for ($i = 0, $length = strlen($roman); $i < $length; $i++) {
            //getting value of current char
            $value = $values[$roman[$i]];
            //getting value of next char - null if there is no next char
            $nextvalue = !isset($roman[$i + 1]) ? null : $values[$roman[$i + 1]];
            //adding/subtracting value from result based on $nextvalue
            $result += (!is_null($nextvalue) && $nextvalue > $value) ? -$value : $value;
        }
        return $result;
    }
}



回答4:


Quick idea - go through the Roman number from right to left, if value of $current (more to the left) is smaller than $previous, then subtract it from the result, if larger, then add it.

$romanValues=array(
    'I' => 1,
    'V' => 5,
    'X' => 10,
    'L' => 50,
    'C' => 100,
    'D' => 500,
    'M' => 1000,
);
$roman = 'MMMCMXCIX';

// RTL
$arabic = 0;
$prev = null;
for ( $n = strlen($roman) - 1; $n >= 0; --$n ) {
    $curr = $roman[$n];
    if ( is_null($prev) ) {
        $arabic += $romanValues[$roman[$n]];
    } else {
        $arabic += $romanValues[$prev] > $romanValues[$curr] ? -$romanValues[$curr] : +$romanValues[$curr];
    }
    $prev = $curr;
}
echo $arabic, "\n";

// LTR
$arabic = 0;
$romanLength = strlen($roman);
for ( $n = 0; $n < $romanLength; ++$n ) {
    if ( $n === $romanLength - 1 ) {
        $arabic += $romanValues[$roman[$n]];
    } else {
        $arabic += $romanValues[$roman[$n]] < $romanValues[$roman[$n+1]] ? -$romanValues[$roman[$n]] : +$romanValues[$roman[$n]];
    }
}
echo $arabic, "\n";

Some validation of roman number should also be added, though you said that you already have found how to do it.




回答5:


Copyrights is for this blog (btw!) http://scriptsense.blogspot.com/2010/03/php-function-number-to-roman-and-roman.html

<?php

function roman2number($roman){
    $conv = array(
        array("letter" => 'I', "number" => 1),
        array("letter" => 'V', "number" => 5),
        array("letter" => 'X', "number" => 10),
        array("letter" => 'L', "number" => 50),
        array("letter" => 'C', "number" => 100),
        array("letter" => 'D', "number" => 500),
        array("letter" => 'M', "number" => 1000),
        array("letter" => 0, "number" => 0)
    );
    $arabic = 0;
    $state = 0;
    $sidx = 0;
    $len = strlen($roman);

    while ($len >= 0) {
        $i = 0;
        $sidx = $len;

        while ($conv[$i]['number'] > 0) {
            if (strtoupper(@$roman[$sidx]) == $conv[$i]['letter']) {
                if ($state > $conv[$i]['number']) {
                    $arabic -= $conv[$i]['number'];
                } else {
                    $arabic += $conv[$i]['number'];
                    $state = $conv[$i]['number'];
                }
            }
            $i++;
        }

        $len--;
    }

    return($arabic);
}


function number2roman($num,$isUpper=true) {
    $n = intval($num);
    $res = '';

    /*** roman_numerals array ***/
    $roman_numerals = array(
        'M' => 1000,
        'CM' => 900,
        'D' => 500,
        'CD' => 400,
        'C' => 100,
        'XC' => 90,
        'L' => 50,
        'XL' => 40,
        'X' => 10,
        'IX' => 9,
        'V' => 5,
        'IV' => 4,
        'I' => 1
    );

    foreach ($roman_numerals as $roman => $number)
    {
        /*** divide to get matches ***/
        $matches = intval($n / $number);

        /*** assign the roman char * $matches ***/
        $res .= str_repeat($roman, $matches);

        /*** substract from the number ***/
        $n = $n % $number;
    }

    /*** return the res ***/
    if($isUpper) return $res;
    else return strtolower($res);
}

/* TEST */
echo $s=number2roman(1965,true);
echo "\n and bacK:\n";
echo roman2number($s);


?>



回答6:


I'm late to the party, but here's mine. Assumes valid Numerals in the string, but doesn't test for a valid Roman number, whatever that is...there doesn't seem to be a consensus. This function will work for Roman numbers like VC (95), or MIM (1999), or MMMMMM (6000).

function roman2dec( $roman ) {
    $numbers = array(
        'I' => 1,
        'V' => 5,
        'X' => 10,
        'L' => 50,
        'C' => 100,
        'D' => 500,
        'M' => 1000,
    );

    $roman = strtoupper( $roman );
    $length = strlen( $roman );
    $counter = 0;
    $dec = 0;
    while ( $counter < $length ) {
        if ( ( $counter + 1 < $length ) && ( $numbers[$roman[$counter]] < $numbers[$roman[$counter + 1]] ) ) {
            $dec += $numbers[$roman[$counter + 1]] - $numbers[$roman[$counter]];
            $counter += 2;
        } else {
            $dec += $numbers[$roman[$counter]];
            $counter++;
        }
    }
    return $dec;
}



回答7:


Just stumbled across this beauty and have to post it all over:

function roman($N)
{
    $c = 'IVXLCDM';
    for ($a = 5, $b = $s = ''; $N; $b++, $a ^= 7)
    {
        for (
            $o = $N % $a, $N = $N / $a ^ 0;

            $o--;

            $s = $c[$o > 2 ? $b + $N - ($N &= -2) + $o = 1 : $b] . $s
        );
    }
    return $s;
}



回答8:


Define your own schema! (optional)

function rom2arab($rom,$letters=array()){
    if(empty($letters)){
        $letters=array('M'=>1000,
                       'D'=>500,
                       'C'=>100,
                       'L'=>50,
                       'X'=>10,
                       'V'=>5,
                       'I'=>1);
    }else{
        arsort($letters);
    }
    $arab=0;
    foreach($letters as $L=>$V){
        while(strpos($rom,$L)!==false){
            $l=$rom[0];
            $rom=substr($rom,1);
            $m=$l==$L?1:-1;
            $arab += $letters[$l]*$m;
        }
    }
    return $arab;
}

Inspired by andyb's answer




回答9:


I just wrote this in about 10 mins, it's not perfect, but seems to work for the few test cases I've given it. I'm not enforcing what values are allowed to be subtracted from what, this is just a basic loop that compares the current letter value with the next one in the sequence (if it exists) and then either adds the value or adds the subtracted amount to the total:

$roman = strtolower($_GET['roman']);

$values = array(
'i' => 1,
'v' => 5,
'x' => 10,
'l' => 50,
'c' => 100,
'd' => 500,
'm' => 1000,
);
$total = 0;
for($i=0; $i<strlen($roman); $i++)
{
    $v = $values[substr($roman, $i, 1)];
    $v2 = ($i < strlen($roman))?$values[substr($roman, $i+1, 1)]:0;

    if($v2 && $v < $v2)
    {
        $total += ($v2 - $v);
        $i++;
    }
    else
        $total += $v;

}

echo $total;



回答10:


function Romannumeraltonumber($input_roman){
  $di=array('I'=>1,
            'V'=>5,
            'X'=>10,
            'L'=>50,
            'C'=>100,
            'D'=>500,
            'M'=>1000);
  $result=0;
  if($input_roman=='') return $result;
  //LTR
  for($i=0;$i<strlen($input_roman);$i++){ 
    $result=(($i+1)<strlen($input_roman) and 
          $di[$input_roman[$i]]<$di[$input_roman[$i+1]])?($result-$di[$input_roman[$i]]) 
                                                        :($result+$di[$input_roman[$i]]);
   }
 return $result;
}



回答11:


function rom_to_arabic($number) {

$symbols = array( 
    'M'  => 1000,  
    'D'  => 500, 
    'C'  => 100, 
    'L'  => 50, 
    'X'  => 10, 
    'V'  => 5, 
    'I'  => 1);

$a = str_split($number);

$i = 0;
$temp = 0;
$value = 0;
$q = count($a);
while($i < $q) {

    $thys = $symbols[$a[$i]];
    if(isset($a[$i +1])) {
        $next = $symbols[$a[$i +1]];
    } else {
        $next = 0;
    }

    if($thys < $next) {
        $value -= $thys;
    } else {
        $value += $thys;
    }

    $temp = $thys;
    $i++;
}

return $value;

}



回答12:


try this simple function

function arabicToRomanNumber($arabicNumber='') {

            $arabicNumValue = intval($arabicNumber);
            $convertedNumber = '';
            $romans = array(
                'M' => 1000, 
                'CM' => 900,
                'D' => 500,
                'CD' => 400,
                'C' => 100,
                'XC' => 90,
                'L' => 50,
                'XL' => 40,
                'X' => 10,
                'IX' => 9,
                'V' => 5,
                'IV' => 4,
                'I' => 1);
            foreach ($romans as $roman => $romanValue) 
            {
                  $matchingNumber = intval($arabicNumValue / $romanValue); // Determine the number of matches
                  $convertedNumber .= str_repeat($roman, $matchingNumber); // Store that many characters
                  $arabicNumValue = $arabicNumValue % $romanValue; // Substract that from the number
            }

            return $convertedNumber;

      }

and finall just pass the arabic numbers as

echo arabicToRomanNumber('25'); //result will be XXV

echo arabicToRomanNumber('250'); //result will be CCL




回答13:


function parseRomanNumerals($input)
{
$roman_val = '';
$roman_length = strlen($input);
$result_roman = 0;
for ($x = 0; $x <= $roman_length; $x++) {
$roman_val_prev = $roman_val;
$roman_numeral = substr($input, $roman_length-$x,1);

switch ($roman_numeral) {
case "M":
$roman_val = 1000;
break;
case "D":
$roman_val = 500;
break;
case "C":
$roman_val = 100;
break;
case "L":
$roman_val = 50;
break;
case "X":
$roman_val = 10;
break;
case "V":
$roman_val = 5;
break;
case "I":
$roman_val = 1;
break;
default:
$roman_val = 0;
}
if ($roman_val_prev<$roman_val) {
$result_roman = $result_roman - $roman_val;
}
else {
$result_roman = $result_roman + $roman_val;
}
}
return abs($result_roman);
}


来源：https://stackoverflow.com/questions/6265596/how-to-convert-a-roman-numeral-to-integer-in-php

标签
php
integer
roman-numerals
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